When the level begins you’ll have access to the infamous Trojan horse. Already inside of the city you can use it to build an army with which you can destroy the Gatehouse. Once you’ve deployed your forces focus all of their strength on the Gatehouse. You have limited resources at this point so it’s important you destroy this target before you run out. Once the Gatehouse is destroyed you’ll gain access to a nearby outpost as well as Achilles and his forces. Gather resources and start bolstering Achilles pre-made army. Once you feel its ready you can start fighting your way to the palace. Deposit Achilles at the palace to win the quest.